Hydrocyclones

ABSTRACT

A hydrocyclone which includes a main body having a chamber therein, the chamber including an inlet section, and a separating section, the separating section having an inner side wall which tapers inwardly away from the inlet section, the hydrocyclone further including a feed inlet feeding a particle bearing slurry mixture into the inlet section of the chamber, an overflow outlet at one end of the chamber adjacent the inlet section thereof, and an underflow outlet at the other end of the chamber remote from the inlet section of the chamber. The hydrocyclone further includes an overflow outlet control chamber adjacent the inlet section of the chamber of the hydrocyclone and in communication therewith via the overflow outlet, the overflow outlet control chamber including a tangentially located discharge outlet and a centrally located air core stabilising orifice which is remote from the overflow outlet.

This invention relates generally to hydrocyclones and more particularly, but not exclusively, to hydrocyclones suitable for use in the mineral and chemical processing industries. The invention is also concerned with components associated with hydrocyclones and methods of optimising their performance.

Hydrocyclones are used for separating suspended matter carried in a flowing liquid such as a mineral slurry into two discharge streams by creating centrifugal forces within the hydrocyclone as the liquid passes through a conical shaped chamber. Basically, hydrocyclones include a conical separating chamber, a feed inlet which is usually generally tangential to the axis of the separating chamber and is disposed at the end of the chamber of greatest cross-sectional dimension, an underflow outlet at the smaller end of the chamber and an overflow outlet at the larger end of the chamber. The feed inlet is adapted to deliver the liquid containing suspended matter into the hydrocyclone separating chamber and the arrangement is such that the heavy matter tends to migrate towards the outer wall of the chamber and towards and out through the centrally located underflow outlet. Finer particle sized material migrates towards the central axis of the chamber and out through the overflow outlet. Hydrocyclones can be used for separation by size of the suspended solid particles or by particle density. Typical examples include solids classification duties in mining and industrial applications.

For enabling efficient operation of hydrocyclones the form of the discharge through the underflow outlet is important. It is known that a hydrocyclone operates more efficiently under a spray discharge at the underflow discharge outlet as opposed to what is known as rope discharge. Spray discharge is where the discharge from the underflow outlet is in the form of an umbrella shaped spray. In a rope discharge the discharge is highly concentrated and tends to choke the underflow outlet diminishing the throughput of the hydrocyclone.

In normal operation such hydrocyclones develop a central air column which is typical of most industrially applied hydrocyclone designs. The air column is established as soon as the fluid at the hydrocyclone axis reaches a pressure below the atmospheric pressure. This air column extends from the underflow outlet to the overflow outlet and simply connects the air immediately below the hydrocyclone with the air at the top. The cross sectional area of the air core is an important factor in influencing the underflow discharge condition which can vary from the typical spray pattern to the extreme condition known as roping. Roping occurs when the solids concentration in the underflow discharge stream reach a critical value and a solid rope of material is discharged. At this condition the air core collapses at the underflow outlet and the underflow outlet discharge capacity is reduced. The reduced discharge capacity compromises the efficiency of the hydrocyclone process and system operating variables are normally required to be changed to reestablish the air core and hence normal hydrocyclone operation.

Existing hydrocyclone designs do not acknowledge the importance of air core cross sectional area or stability of the air column. In most hydrocyclones a simple curved pipe carries away the overflow stream. The air column remains captive within the overflow stream and consequently the air core diameter and hence its cross sectional area remains compressed. Furthermore within the overflow pipe the spinning motion of the overflow stream changes chaotically into linear flow and continuity of the air column is destroyed.

It is an object of the present invention according to one aspect of the invention to provide an improved hydrocyclone in which the air core formed during operation can be stabilised and maximised with respect to its cross sectional area It is another object of the present invention according to a further aspect to provide a method of optimising performance of a hydrocyclone. Yet another object of the present invention according to a further aspect is to provide an overflow control device for use with a hydrocyclone.

According to one aspect of the invention a hydrocyclone is provided with an overflow discharge control chamber with an air core stabilising orifice, the combination of which separates the overflow stream from the air column.

The arrangement as described above in its preferred form has been found to promote a stable cyclone discharge flow, minimise any back pressure on the cyclone system process, maximise the cross-sectional area of the central axial air core generated within the cyclone, maximise throughput of product in terms of, for example, tonnage per hour, and maintain the cyclone separation process at a stable level.

The hydrocyclone can be controlled so as to operate at a steady state and deter the tendency towards the formation of a rope type discharge at the underflow discharge outlet. Regulation of the air inlet flow can be used to influence the formation, maximisation of cross-sectional area and stabilisation of the cyclone air core. Furthermore, the air core stabilising orifice provides the potential opportunity to view the internal operation of the hydrocyclone for more advanced process control as hydrocyclone technology develops.

According to another aspect of the present invention, there is provided a hydrocyclone which includes a main body having a chamber therein, the chamber including an inlet section, and a separating section, the separating section having an inner side wall which tapers inwardly away from the inlet section. The hydrocyclone further includes a feed inlet feeding a particle bearing slurry mixture into the inlet section of the chamber, an overflow outlet at one end of the chamber adjacent the inlet section thereof, and an underflow outlet at the other end of the chamber remote from the inlet section of the chamber. The hydrocyclone further includes an overflow outlet control chamber adjacent to the inlet section of the chamber of the hydrocyclone and in communication therewith via the overflow outlet. The overflow outlet control chamber includes a tangentially located discharge outlet and a centrally located air core stabilising orifice, which is remote from the overflow outlet.

Preferably, the stabilising orifice, overflow outlet and underflow outlet are generally axially aligned.

In one preferred form, the overflow outlet control chamber has an inner surface which is generally in the shape of a volute for directing material entering the overflow outlet control chamber from the separation chamber towards the discharge outlet. Preferably, the volute extends around the inner surface for up to 360°.

In a preferred form of the invention, the inlet section of the chamber has an inner surface which is generally in the shape of a volute and preferably the volute is ramped axially toward the converging end of the separation chamber and extends around the inner surface for up to 360°.

The hydrocyclone may further include a vortex finder at the overflow outlet of the separation chamber.

In one preferred form of the invention, the stabilising orifice comprises tapering side walls which extend into the control chamber. Preferably, the orifice has a generally conical shaped inlet section.

According to yet another aspect of the present invention there is provided a control unit which is suitable for use with a hydrocyclone, the hydrocyclone including a main body having a chamber therein, the chamber including an inlet section and a separating section, the separating section having an inner side wall which tapers inwardly away from the inlet section, a feed inlet for a feeding mixture into the inlet section of the chamber, an overflow outlet at one end of the chamber adjacent to the inlet section and an underflow outlet at the other end of the chamber remote from the inlet section of the chamber. The control unit includes a control chamber having a discharge outlet. a communication port operatively connected to the overflow outlet and a stabilising orifice which is remote from the overflow outlet.

In a preferred form, the control chamber may be in the form described earlier. In addition, the hydrocyclone may be of the type described earlier.

According to yet another aspect of the present invention there is provided a method of stabilising the air core of a hydrocyclone when in use, the method including the steps of providing a chamber above the overflow outlet of a hydrocyclone and arranging for discharge from that chamber through a discharge outlet and incorporating an air core stabilising orifice in a wall of that chamber remote from the overflow outlet.

The arrangement as described above in its preferred form has been found to promote a stable cyclone discharge flow, minimise any back pressure on the cyclone system process, maximise the cross-sectional area of the central axial air core generated within the cyclone, maximise throughput of product in terms of, for example, tonnage per hour, and maintain the cyclone separation process at a stable level.

The hydrocyclone can be controlled so as to operate at a steady state and deter the tendency towards the formation of a rope type discharge at the underflow discharge outlet. Regulation of the air inlet flow can be used to influence the formation, maximisation of cross-sectional area and stabilisation of the cyclone air core. Furthermore, the air core stabilising orifice provides the potential opportunity to view the internal operation of the hydrocyclone for more advanced process control as hydrocyclone technology develops.

Preferred embodiments of the invention will hereinafter be described with reference to the accompanying drawings and in these drawings:

FIG. 1 is a schematic partial sectional view of a hydrocyclone according to the present invention;

FIG. 2 is a plan view of the hydrocyclone shown in FIG. 1; and

FIG. 3 is a schematic sectional side elevation showing several key dimensions.

Referring to the drawings, there is shown a hydrocyclone generally indicated at 10 which includes a main body 12 having a chamber 13 therein, the chamber 13 including an inlet section 14, and a conical separating section 15. The hydrocyclone further includes a feed inlet 17 feeding a particle bearing slurry mixture into the inlet section 14 of the chamber. An overflow outlet or vortex finder 27 is provided at one end of the chamber adjacent the inlet section thereof, and an underflow outlet 18 at the other end of the chamber remote from the inlet section of the chamber. The hydrocyclone further includes a control unit 20 having an overflow outlet control chamber 21 adjacent the inlet section of the chamber of the hydrocyclone and in communication therewith via the overflow outlet. The overflow outlet control chamber includes a tangentially located discharge outlet 22 and a centrally located air core stabilising orifice 25 which is remote from the overflow outlet. The stabilising orifice, overflow outlet and underflow outlet are generally axially aligned.

The overflow outlet control chamber 21 has an inner surface which is generally in the shape of a volute for directing material entering the overflow outlet control chamber from the separation chamber towards the discharge outlet. Preferably, the volute extends around the inner surface for up to 360°.

The inlet section 14 of the chamber 13 of the hydrocyclone has an inner surface, which is generally in the shape of a volute and preferably the volute is ramped axially toward the converging end of the separation chamber and extends around the inner surface for up to 360°.

The stabilising orifice 25 comprises tapering side walls which extend into the control chamber, which as shown form a generally conical shaped inlet section. The control unit 20 may be integral with the hydrocyclone or separate therefrom so that it enables it to be retrofitted to existing hydrocyclones.

FIG. 3 of the drawings indicates several dimensions of the hydrocyclone, which can influence the operation thereof These are defined as follows:

-   -   D_(J)=diameter of the feed inlet     -   D_(U)=diameter of the underflow outlet     -   D_(O)=diameter of the overflow outlet     -   D_(S)=diameter of the stabilising orifice     -   D_(C)=diameter of the inlet section of the hydrocyclone chamber     -   L₁=overall length of the hydrocyclone

Examples of preferred ratios of these dimensions are set out below.

-   -   Dj=0.20 to 0.34 Dc     -   Do=0.20 to 0.45 Dc     -   Du=0.30 to 0.75 Do     -   L1=3.0 to 8.0 Dc     -   Ds=0.0 to 1.0 Do

Finally, it is to be understood that various alterations, modifications and/or additions may be incorporated into the various constructions and arrangements of parts without departing from the spirit or ambit of the invention. 

1. A hydrocyclone which includes a main body having a chamber therein, the chamber including an inlet section, and a separating section, the separating section having an inner side wall which tapers inwardly away from the inlet section, the hydrocyclone further including a feed inlet feeding a particle bearing slurry mixture into the inlet section of the chamber, an overflow outlet at one end of the chamber adjacent to the inlet section thereof and an underflow outlet at the other end of the chamber remote from the inlet section of the chamber, the hydrocyclone further including an overflow outlet control chamber adjacent to the inlet section of the chamber of the hydrocyclone and in communication therewith via the overflow outlet, the overflow outlet control chamber including a tangentially located discharge outlet and a centrally located air core stabilising orifice which is remote from the overflow outlet.
 2. A hydrocyclone according to claim 1 wherein the stabilising orifice, overflow outlet and underflow outlet are generally axially aligned.
 3. A hydrocyclone according to claim 2 wherein the overflow outlet control chamber has an inner surface which is generally in the shape of a volute for directing material entering the overflow outlet control chamber from the separation chamber towards the discharge outlet.
 4. A hydrocyclone according to claim 3 wherein the volute extends around the inner surface for up to 360°.
 5. A hydrocyclone according to claim 4 wherein the inlet section of the chamber has an inner surface which is generally in the shape of a volute, the volute being ramped axially toward the converging end of the separation chamber and extends around the inner surface for up to 360°.
 6. A hydrocyclone according to claim 5 further including a vortex finder at the overflow outlet of the separation chamber.
 7. A hydrocyclone according to claim 6 wherein the stabilising orifice comprises tapering side walls which extend into the control chamber.
 8. A hydrocyclone according to claim 7 wherein the orifice has a generally conical shaped inlet section.
 9. A control unit which is suitable for use with a hydrocyclone, the hydrocyclone including a main body having a chamber therein, the chamber including an inlet section and a separating section, the separating section having an inner side wall which tapers inwardly away from the inlet section, a feed inlet for a feeding mixture into the inlet section of the chamber, an overflow outlet at one end of the chamber adjacent the inlet section and an underflow outlet at the other end of the chamber remote from the inlet section of the chamber, the control unit including a control chamber having a discharge outlet. a communication port operatively connected to the overflow outlet and a stabilising orifice which is remote from the overflow outlet.
 10. A control unit according to claim 9 wherein the overflow outlet control chamber has an inner surface which is generally in the shape of a volute for directing material entering the overflow outlet control chamber from the separation chamber towards the discharge outlet.
 11. A control unit according to claim 10 wherein the volute extends around the inner surface for up to 360°.
 12. A control unit according to claim 11 wherein the stabilising orifice comprises tapering side walls which extend into the control chamber.
 13. A control unit according to claim 12 wherein the orifice has a generally conical shaped inlet section.
 14. A method of stabilising the air core of a hydrocyclone when in use, the method including the steps of providing a chamber above the overflow outlet of a hydrocyclone and arranging for discharge from that chamber through a discharge outlet and incorporating an air core stabilising orifice in a wall of that chamber remote from the overflow outlet. 